Chronic electrical stimulation of the cerebellum has been performed to reduce spasticity in brain-damaged patients. The purpose of our proposed study is to investigate the physiology of spasticity and to attempt to evaluate the efficacy of electrical stimulation as a therapeutic procedure. We plan to define rigorously the elements of spasticity and evaluate motor control in cerebral palsy, spinal cord injury, and stroke patients. Tests of fine and gross motor control, simple tracking movements, and tests to elicit developmental reflexes, muscle rigidity, phasic stretch reflexes, and "long loop" late reflexes will be performed. The cerebellar implant patients will also be evaluated with these tests in our continuing double-blind studies. We hope to relate the specific motor impairments in the patients with damage of the central nervous system to the underlying neurophysiological abnormalities. Furthermore, we hope to correlate any functional improvement which may occur with cerebellar stimulation to physiological changes.